Fix garbage character in panel_test.extjs

TBR=dtseng@chromium.org

Change-Id: Ie4a1691308224d015856d93cbee256f6420a0b51
Reviewed-on: https://chromium-review.googlesource.com/1246663Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594464}

chrome/browser/resources/chromeos/chromevox/cvox2/background/panel_test.extjs

@@ -23,7 +23,7 @@ PanelTest.prototype = {
   testGenCppIncludes: function() {
     ChromeVoxE2ETest.prototype.  testGenCppIncludes.call(this);
 
-    -// Flaky on dbg, see https://crbug.com/795840
+    // Flaky on dbg, see https://crbug.com/795840
     GEN_BLOCK(function() { /*!
 
 #if !defined(NDEBUG) || defined(MEMORY_SANITIZER)